Tale teller is explicit: nothing's up (8)
I believe the answer is:
franklin
'tale teller' is the definition.
(character in Chaucer's Canterbury Tales)
'explicit nothing's up' is the wordplay.
'explicit' becomes 'frank' (frank can mean direct or explicit).
'nothing' becomes 'nil' (eg nil is zero in football).
'up' is a reversal indicator (in down clue: letters go upwards).
'nil' written backwards gives 'lin'.
'frank'+'lin'='FRANKLIN'
'is' acts as a link.
(Other definitions for franklin that I've seen before include "Statesman" , "One with a tale to tell" , "old landowner" , "[PILGRIM in the CANTERBURY TALES]" , "Tale-bearer" .)